“Are you with the extremist groups who wear some logos and emblems that look like Nazi style emblems on them? Are you with them? Are you with the extremists who are attacking the police with Molotov cocktails?” he demanded to know.

Klitschko did not reply – but did speak outside before a small group of opposition supporters, whose banners included a message warning Russia’s President Putin not to touch Ukraine.

Speaking in German, the former boxing champion said: “We have enough of crime, enough of corruption, enough of waiting for a better future. We are patient enough, but we cannot wait any longer.”

Opposition leaders have said they welcome “huge support” from the EU – which says closer ties are still on offer – and from the US.

Visiting US Senator John McCain confirmed that Washington was preparing sanctions that would soon hit oligarchs and others.

“I think it would probably be the most effective way of at least preventing some of the violence that’s going on. We (Congress) are already in the process of preparing sanctions and the administration is too and we will be working with the administration,” the Republican senator told euronews.

According to Germany’s Foreign Minister Frank-Walter Steinmeier, his Ukrainian counterpart has agreed to allow Dmytro Bulatov – who faces house arrest on disorder charges – to go abroad for medical treatment.